Band-pass filter

Abstract

The present invention provides a band-pass filter having: a first substrate; a second substrate; an input line; an output line; a ground layer; and an electromagnetic wave absorptive layer, the input line being provided on a first surface of the first substrate, the input line extending from a first edge thereof toward a second edge thereof, the output line being provided on a second surface of the first substrate, the output line extending from the second edge thereof toward the first edge thereof, the input line and the output line forming an overlapping line, the output line being sandwiched between a first surface of the second substrate and the second surface of the first substrate, the ground layer being provided on a second surface of the second substrate; the electromagnetic wave absorptive layer being provided on the first surface of the first substrate, the electromagnetic wave absorptive layer covering the input line.

1. A band-pass filter comprising:
 a first substrate; 
 a second substrate; 
 an input line; 
 an output line; 
 a ground layer; and 
 an electromagnetic wave absorptive layer, 
 the input line being provided on a first surface of the first substrate, the input line extending from a first edge thereof toward a second edge thereof, 
 the output line being provided on a second surface of the first substrate, the output line extending from the second edge thereof toward the first edge thereof, the input line and the output line forming an overlapping line, 
 the output line being sandwiched between a first surface of the second substrate and the second surface of the first substrate, 
 the ground layer being provided on a second surface of the second substrate; 
 the electromagnetic wave absorptive layer being provided on the first surface of the first substrate, the electromagnetic wave absorptive layer covering the input line; 
 wherein the electromagnetic wave absorptive layer is a synthetic resin matrix having a soft magnetic metal powder dispersed therein. 
 
   
   
     2. The band-pass filter according to  claim 1 ,
 wherein a complex relative permittivity of the first substrate is an integral multiple of a complex relative permittivity of the second substrate. 
 
   
   
     3. The band-pass filter according to  claim 1 ,
 wherein a length of the overlapping line is set by the following equation:
     fn=K ×( C   0   /L ) 
 
 
     wherein fn denotes the notch frequency, K denotes the substrate factor, C 0  denotes the speed of light, and L denotes the length of the overlapping line. 
   
   
     4. The band-pass filter according to  claim 1 ,
 wherein the first substrate and the second substrates are ceramic substrates. 
 
   
   
     5. The band-pass filter according to  claim 1 ,
 wherein the synthetic resin matrix is a liquid-crystal polymer. 
 
   
   
     6. The band-pass filter according to  claim 1 ,
 wherein the soft magnetic metal powder is dispersed in the synthetic resin matrix in the amount of  5 % by volume. 
 
   
   
     7. The band-pass filter according to  claim 1 ,
 wherein the electromagnetic wave absorptive layer is electrically isolated from the ground layer. 
 
   
   
     8. The band-pass filter according to  claim 2 ,
 wherein a ratio of the complex relative permittivity of the first substrate to the complex relative permittivity of the second substrate is 2:1.